Air traffic fault at Prestwick delays Scotland flights
The UK’s air traffic control provider said the Prestwick fault had nothing to do with the failure on 8 September, which a preliminary report traced to a software defect.
A network fault at NATS’s Prestwick air traffic control centre in Scotland forced flight restrictions and delays on 21 September and has now been fixed, the UK’s air traffic control provider has said.
The fault began early that morning, and air traffic regulations were applied to manage traffic demand while engineers investigated, to maintain safety.
“The issue has now been fixed and we are running at full capacity,” NATS said, adding that it was working with its customers “to recover their residual delays and help get their operations back to normal”.
It did not say which airports or how many flights were affected. The fault, it added, was “nothing to do with the problem we had earlier this month” – a reference to a failure on 8 September.
What the 8 September report found
That earlier failure led to a preliminary report which NATS published on 18 September at the request of Heidi Alexander, Secretary of State for Transport, with a full report to follow.
The report said the incident was caused by a software defect in a small part of the National Airspace System (NAS), which underpins the management of UK airspace.
The software allocates the codes used to identify individual aircraft on radar; these are usually allocated automatically, but can be requested manually.
A manual request for an aircraft code was paused when the system received a message for a higher priority activity. When processing resumed, “it did not resume correctly and the resulting output was corrupted”, affecting some flight data updates – a fault that occurred “in the space of a millisecond”.
Although the software issue affected only flights handled by the London Area Control centre – higher level flights operating mainly above 24,500ft – restrictions had to be applied across the UK so that the system could be restarted and flight data reloaded.
Restrictions were in place for some six hours. Operations returned to normal the same evening, but it took more than two days for the backlog to clear, with hundreds of thousands of passengers’ travel plans disrupted.
Martin Rolfe, NATS chief executive, said the failure was unrelated to the company’s major system outage in August 2023 and dismissed speculation that it had been caused by military intervention.
“This was a software issue in a specific part of our flight data system, that we have traced to a small subsection of coding,” Rolfe said, adding that mitigation was in place “while a permanent fix is safety tested and deployed”.
NATS said it had invested “well over one billion pounds” in systems and technology over the past 10 years, and would soon submit plans to the Civil Aviation Authority to invest a further £1bn by the end of 2033.
In the preliminary report published on 18 September, Rolfe said: “I would like to apologise again, very sincerely, to everyone who was affected”, adding that “at no point last week was safety in question”.
